Sandblasting is one of the conventionally known processing methods for patterning the surface of a substrate such as glass, stone, plastics, ceramics, leather, andwood. The sandblasting is a processing method wherein a rubber sheet, paper or the like is pasted on the surface of a substrate and cut out to conduct patterning, then an abrasive or the like is blown against the patterned surface to selectively engrave the substrate. In particular, a sandblasting method, in which a mask pattern is formed in a photosensitive composition layer for sandblasting formed on the surface of a substrate by photolithography and selective engraving is conducted by blowing an abrasive material or the like (hereinafter referred to as “sandblasting method based on photolithography”), provides a high working efficiency and permits fine processing, thus being effective for formation of a circuit board where a metal pattern and an insulation pattern coexist, especially for formation of a metal wiring pattern or an insulation pattern made of ceramics, fluorescence substances, etc. of a plasma display.
Photosensitive compositions for sandblasting utilizing the lithography which have been proposed to date for use in sandblasting include a photosensitive composition containing a urethane prepolymer having an ethylenically unsaturated group at the terminal, a mono-functional ethylenically unsaturated compound and a polymerization initiator (JP-A-60-10242 (The term “JP-A” as used herein means an “unexamined published Japanese patent application”)), a photosensitive composition containing an unsaturated polyester, an unsaturated monomer and a photopolymerization initiator (JP-A-55-103554), and a photosensitive composition comprising polyvinyl alcohol and a diazo resin (JP-A-2-69754). However, the above-described photosensitive resin compositions have the defects that film thickness control is difficult, that sensitivity, adhesion to a substrate and sandblast resistance are insufficient, and that fine processing is difficult.
As a photosensitive composition for sandblasting, which is free from the above defects, the applicant has formerly proposed in JP-A-6-161098 a photosensitive composition for sandblasting which mainly comprises a urethane oligomer having an ethylenically unsaturated group at the terminal and having incorporated therein a cellulose derivative and a polymerization initiator. While this photosensitive composition for sandblasting described in JP-A-6-161098 has an excellent alkali developability and is superior to the conventional ones in sensitivity, adhesion to a substrate, elasticity and flexibility after patterning, and sandblasting resistance, it is still insufficient in putting fine processing into practice. In addition, the cellulose resin used as abase resin is so expensive that the resulting photosensitive composition is costly. Hence, it has been attempted to develop a photosensitive composition capable of being put into practice by using a less expensive acrylic resin but, since the acrylic resin has a poor compatibility with a urethane oligomer, particularly a urethane oligomer having polyether structural units, formation of a good pattern has been difficult.